Frequency indicator



OCt. ll, G. w FREQUENCY INDICATOR Filed April 23, 1928 esrsnr @EQRGE W. PINE, Q15 CAMRXDG'E, HASCHUQETES KEEQUENGY HIYDICAZQR Appiloerlon filed April 23, 1928, serial No. 272,083, and in Granada December 81, 1993?.

The present invention relates to electrical systems and apparatus and more particularly to frequency indicators.

A chief object or the invention is to pro- 5 vide e new and improved frequency indicat-or.

With this and other objects in view, the invention consists of the improved frequency indicator a preferred embodiment of which is hereinafter descrihed, illustrated in the accompanying dressing and defined in the appended claims.

The invention. will be ezpleined in greater detail in connection wit he accompanyi g drawing, in which l is e diagrammatic view appsrm-us circuits constructed and srrsnged illustrate principle of oresent invention; rigs. 2

id Q are plots oz ezperimental results; ans is e disg metic similar to a modific on.

" tcstricfvs vibrators, as is explained Patent No. 1350,1544 granted erisl No. ed J nuary 3, 1927, of which the n is a continuation in part,

constituted of s megnetostrictive core 2 i 'n an electromagnetic field, such produced a coil or winding in we core deformed or distorted by i lne resuif r. tog, or some other on the r s te rial a increment or one magneti g increment suing, or distortion, clepolarity Eon e .i wing core, and the core reschly recovers upon the with rawal of def ing forces.

it the current or volt-s e is alternating, the electromagnetic field created thereby will 50 also be alternating. The core 2 "will, therefore, increase and decrease in length (let us say) many times a second, every variation in the current producing its stimulati ve efiect on the core 2, and every deformation of the core producing its reaction response upon the current. The core 2 will, in consequence, vibrate mechanically by magnetostriction about a nodal point at its center with a period of vibration equal to'the period of the alternating electrornotive force. Grdinarily, these vibrations will be quite small. "W hen the alternating frequency is close to, or substantially the s me as, the natural frequency of mechanical vibration of the core 2, however, the amplitude of vilzration oi the core, though still small, becomes relatively quite large. The core will then inductively on the load to render its consumption of power critical as to frequency for frequencies near the free -irequiency oi the core. The mechanicel damping of the core, mounted as shown, is as small as possible, with the result that the resonant response of the core is very sharp and pronounced.

To illustrate the principle of the invention, the magnetostrictive core 2 is shown in Fig. l driven by a solenoid coil 10 provided with conductors l2 and let by which it may he connected, for simplicity, in series with a source oft alternating electronic-five force, such as an alternating current generator 16. (lther, more complicated, sources of alternating cur rent may he used, one of which is illustrated in Fig. A local battery 18 (shown in Fig. 1 in series with the source 16 and the winding 10) applies a steady magnetizing field to the core 2, over which the alternating field pro duced by the generator 18 is superposed. The alternating field is preferably smaller than the steady field, in order that the combined fields may not, at any time, fa l to zero. The battery may be dispensed with, and the core may he magnetized electro-inagnetically by a local source, or it may be permanently magnetized, instead, or the battery and a permanently magnetized core may be employed together.

In order not to complicate the showing of Fig. 1, no means are illustrated therein for tuning the circuit or varying the frequency of the alternating current flowing therein, particularly as the core 2 may itself be atuned element of very low decrement, thereby dispensing with or supplementing electrical tuning of the circuits. An important feature of the invention contemplates the use of a tuned system, as great frequency selectivity is thereby attained, and it will be understood that a tuning condenser or other tuning device may be used to efi'ect this result. If the frequency of the alternating current is varied gradually by this tuning device, or by variation of the speed of the generator, from a value on one side of the natural or resonant frequency of mechanical vibration'of the core, to a value on the other side of this frequency, a comparatively intense sound is produced somewhere in this range, if the resonant frequency is within audible limits. If the frequeneyis outside the audible range, the resonant response is made manifest by a transient sound, or click, in the telephones, or by a change n the reading of an annneter 20 connected in circuit. This resonant response takes place whenever the tuning of the electromoti ve force passes through values synchronous with the period of the vibrator, setting the vibrator into violent vibration; or, in more technlcal language, the approximate equality of the frequency of the applied electromotivc force and that of the core is indicated by singular values of the impedance of the system. The invention, therefore, finds application as a very accurate frequency indicator. By filing the resonator down, or adding to its mass by solder or plating, any desired frequency may readily be attained, either high or low, and the frequency indicators calibrated accordingly. Once calibrated by comparison with a standard frequency meter, they will then serve as very accurate frequency indicators themselves. Further illustrations of this'operation will appear'in connection with a disquency of the core.

cussion of the other fi ures of the drawing.

The operation will e better understood in connection with the plot of Fig. 2, showing the relation between the resistance R and the reactance Lo of the winding 10 for difference frequencies of applied electromotive force in the neighborhood of the natural or free fre- The axis of abscissae represents the applied frequency 7' (number of cycles per second) of the electromotive force,

- and the ordinate is, in the case of one curve,

the reactance Lo, and in the other, the resist ance R, both measured in ohms. m is an abbreviation for 21f. The particular core employed in the experiment was of nickel-steel, about 0.92 cm. long, and had a free frequency of fundamental longitudinal vibration of about 2290 cycles per second. As the curves of Fig. 2 clearly show, the reactance Lu) and the resistance R undergo marked effects, the former sinking to a minimum in the neighborhood of the resonant frequencyof the core, I

and the latter at a frequency somewhat greater.

In Fig. 3, the total impedance Z of the I the sum of the squares of the resistance R and the reactance Lo of Fig. 2. According to this plot, the impedance Z of the winding 10 is at a minimum at a frequency of about 2291 cycles per second. The ammeter 20 in the circuit of 1g. 1 will therefore indicate a maximum of current when the generator frequency has this value.

lln the neighborhood of this resonant frequency, the power output of the generator undergoes a large increase. Assuming, therefore, that the generator is running at a speed a little too slow to give maximum power, and that the generator increases in speed, the draft of power from the enerator by the load will increase, and ten to slow the generator down. If, on the other hand, the generator speed tends to decrease, the load will decrease also, and this will tend to maintain the generator speed high. The vibration of the magnetomechanical vibrator thus acts to stabilize the generator, as .ex-, plained in the said Letters Patent.

Any material having suitable properties 7 may, of course, be used for the vibrating body 2, but it should obviously be constituted of material that is suitably magnetizable. Thecore may be in the form of a simple rod or.

tube of the proper material; but'to obtain Different bodies possess the requisite in proper proportions, have comparatively large magnetostriction. Thus, alloys consisting of iron and chromium, or nickel and chromium, nickel and cobalt, or nickel and iron, also nickel and copper, form very good magnetostrictive vibrators. or more of these elements may also be advantageously employed. Cores of nickel, nickel steel and chrome steel have large magnetostrictive effects. Ordinary metals have their elasticity and density slightly modifiable by changes in temperature. Such temperature char. ges, therefore, introduce small variations in the natural period of mechanical vibration of such bodies. To obtain substantially constant frequency, it is preferred to utilize a vibrator having a coefficient of the ratio of elasticity to density that varies as little as Alloys of three lessees 7 possible with variations of tem rature. Cerwide limits. Annealed rods, accordin tain alloys of steel, nickel an chromium are known to possess substantial] constant coeficients of frequencywith variations of temperature. One such alloy, constituted of 52% iron, 36% nickel and 12% chromium, is practically independent of tern erature. I have found that a rod of nicke chromium and steel has a period that is also practically independent of magnetic field strength over to my experiments, 've the best results. or high precision of requency, the metal should have a high constancy of elasticity.

If the vibrator is in the form of a rod or tube of small diameter, the period of vibration is nearly proportional to the length of the rod or tube. Thus, a rod of nickel-steel, known in the trade as stoic metal, having a diameter of one-half centimeter and a length of ten centimeters, has a fundamental period of longitudinal vibration of about 1/21,000 of a second. A rod of the same diameter ten times as long centimeters) has a period about 1/2100 of a second. Rods of the same diameter and the same two respective lengths, but constituted of an alloy of iron and chromium in a particular proportion, heve the fundamental periods of 1/27,000 and 1/2700 oi a second, respectively. These results are consistent with the fact that the two materials have difierent elasticities and densities.

The above figures correspond to but a single mode of vibration or the cores. But all vibratory bodies have also additional modes of vibration. In addition to one or more natural fundamental frequencies of mechanical vibration, the core has also frequencies of vibration determined by the operation of the core in halves, thirds, iourths, fifths and other overtones. There will usually, therefore, be more than one specific frequency of magnetization at which the core will resonate as above described. Such other modes of vibration may be produced by particular methods of stimulating the vibrations, or b particular modes of clamping the body. n addition to other modes of longitudinal vibration, there are certain magnetostrictive efiects attendant upon the twist or torsion of the cores, particularly if current be sent lengthwise through the core, so that torsional vibrations are also available. All these modes and kinds of vibration may be utilized according to the present invention.

1 find that at frequencies as high as 200,000 cycles per second, a solid nickel-steel, nichrome, or chromium-steel rod is highly ellicient even when its diameter is as large as 1 inch, and though used in magnetizing coils that have a clearance of more than 4 inch all around the rod. By diminishing this clearance and using cores of smaller diameter and shorter lengths, the upper limit of frequency can be greatly raised, and then I properl constructed comminuted cores with elastic inding material will serve still further to raise the limit of available frequencies.

It will be noted that when vibrating at its fundamental frequency, the two halves of the centrally supported core are driven by equal and oppositely acting forces, so as to communicate practically no motion to the clamp and its base. The apparatus is, therefore, free from one of the sources of trouble and irregularity of tuning forks,the periods of vibration of which are affected by the table or other support on which they are placed. The centrally supported vibrator of the present invention is not dulled, as is a tuning fork, by its own resonance,-a very important consideration where tuned vibrators are necessar go well does the resent vibrator balance itself about a centre pivot 6 that I find that the clamp 6, 8, shown in Figs. 1 and 4, between which the core is centrally clamped, may be dispensed with and a mere pivot rest 6 take its place, as shown in the before-mentioned Letters Patent, upon which the core freely rests centrally. With this arrangefield, here shown as produced by coils 22 and 2 1-, and is preferably held in such manner, as by means of the centrally positioned clamps 6 and 8, as freely to vibrate longitudinally about a nodal point at its center. For symmetry, one of the coils is positioned on one side of the middle of the core 2 and the other on the other side. The coils may be compacted near the center of the core, or they may be separated or spread out, each over the Whole region of the half-length of the core,

or they may be replaced by a single coil. The

coil 22 is connected, in series with the local batter 18, between the filament or cathode 26 an the plate or anode 28, in the output or plate circu1t of a vacuum tube 30. The coil 24 is similarly connected in the in ut or grid circuit of the tube, between the lament 26 and the grid or third electrode 32. The coils 22 and 24 thus form electrical paths between the filament and the plate, and between the filament and the grid, respectively. The rid and the plate may, if desired, be spanned y a variable condenser 34; or the tuning condenser me" be connected in parallel with one or the output circuit to the input circuit. This transformation of energy is effected, at constant frequency, through the effects produced by the distortion or deformation of the core,

' as is explained in the said Letters Patent.

The tuning is such that high selectivity of frequency is possible in the transfer of energy from one circuit to another. The local battery 18 may serve to supply the plate current, as well as to polarize the vibrator. For highfrequency oscillations, the winding of one of the coils 22 and 24 may be reversed as compared with the other winding, and as compared with the arrangement of oscillators of this character as usually constructed. The reversal of the coil is not necessar in all cases, but it has the advantage of ma ing the oscillations much larger and more stable and preventing parasitic electric oscillations by electric feed back and of restricting the oscillations to periods determined by the me chanically-tuned core.

The operation is fully described in the said Letters Patent but, of course, the operativeness of the invention does not depend upon the theories that may be advanced to explain it.

By proper choice of length and other dimensions, as explained in the said Letters Patent, the apparatus is applicable to systerns of high or low frequency within a range that may extend from a hundred cycles to hundreds of thousands of cycles.

It will be clear that instead of the funda- -mental frequency, any harmonic of the resultant electrical oscillations may be utilized; and, vibrations other than the fundamental longitudinal frequency of the core may also be employed.

To persons skilled in the art many modifications of the apparatus will occur, and no effort has here been made to be exhaustive.

What is claimed is:

1. A frequency indicator comprising an alternating-current circuit having a coil, and a magnetostrictive vibrator centrally balanced in the coil adapted to vibrate about its cenmr, the vibrator being adapted to vibrate mechanically by magnetostriction wh'hn stimulated magnetically by theelectromagnetic field of the coil and to react magnetically through magnetostrictive efiects upon the current in the coil when vibrated, and means for indicating the magnetostrictive reaction of the vibrator upon the current in the coil.

2. A frequency-indicatin body having me. etostrictive activity, in combination wit an exciting circuit therefor, the relation between the body and the circuit being such that the current flowing through the circuit is subjected to the reaction of the body due to magnetostrictive effects, and means for indicating the said reaction in the said circuit.

3. A frequency-indicating body having high magnetostrictive roperties and having as its frequency of vi ration the frequency 'of longitudinal vibration, in combination with an exciting circuit therefor, the relation between the body and the circuit being such that the current flowing through the circuit is subjected to the reaction of the body due to magnetostrictive efiects, and means for indicating the said reaction in the said circuit.

4. A' magnetostrictive frequency-indicating body mounted to vibrate symmetrically about its center, in combination with an exciting circuit therefor, the relation between the body and the circuit being such that the current flowing through the circuit is subjected to the reaction of the body due to magnetostrictive effects, and means for indicating the said reaction in the said circuit.

5. A magnetostrictive frequency-indicating body, in combination with a support upon which it freely: rests to vibrate, and an exciting circuit therefor, the relation between the body and the circuit being sucn that the current flowing through the circuit is subjected to the reaction of the body due to magnetostrictive efiects, and means for indicating the said reaction in the said circult.

6. A frequency indicator comprising a magnetostrictive core capable of resonating to specific fixed frequencies of magnetization, in combination with an exciting circuit therefor, the relation between the core and the circuit being such that the current flowing through the circuit is subjected to the reaction of the core due to magnetostrictive effects, and means for indicating the said reaction in the said circuit.

7. A frequency indicator comprising a magnetostrictive vibrator capable of free mechanical vibration of small decrement, in combination with an exciting circuit therefor, the relation between the vibrator and the circuit being such that the current flowing through the circuit is subjected to the reaction of the vibrator, and means for indicating the said reaction in the said circuit.

8. A frequency indicator comprising a circuit having a source of electric oscillations of variable frequency, a magnetostrictive body connected to said source so as to be ex cited thereby, the relation between the body and the circuit being such that the current flowing through the circuit is subjected to the reaction of the body due to magnetostrictive efiects at a predetermined frequency of the oscillations of the circuit, and means for ina dicating the said reaction in the said circuit.

9. A frequency indicator comprising a frequency-standard, magnetostrictive vibrator having a natural frequency of mechanical vibration, in combination with an exciting m circuit therefor, the relation between the vibrator and the circuit being such that the current flowing through the circuit is subjected to the reaction of the vibrator due to magnetostrictive ettects, means for varying 15 the frequency of the current in the circuit so that said frequency will be in substantial resonance with the vibrator, and means for indicating the said reaction in the said circuit. 10. An electric system comprising an elec 2a tric circuit having a winding for the fiow of alternating current and a tuned magnetostrictive vibrator core so associated with the electromagnetic field of the winding that it freely vibrates mechanically by magnetoae striction when stimulated magnetically by the said field,.and means in the circuit for utilizing the power when the core, freely vibrating mechanically, responds magnetostrictively, rendering the power in the said so circuit critical as to frequency for frequencies near the free frequency of t e core.

11. An electric system as defined in claim 10 in which the core is freely supported upon a support. as 12. An electric system as defined in claim 10 in which the core is centrally supported to vibrate symmetrically about its central support.

13. An electric system as defined in claim 10 in which the winding is connected in circuit with a generator.

14. An electric system as defined in claim. 10 in which the ,core is weighted.

15. An electric system as defined in claim 10 in which the core is polarized.

, 16. The combination with'a circuit having means for producing an alternating magnetic field, of a magnetostrictive vibrator substantially resonant with the said field, the

vibrator being so associated with thesaid field that it freely vibrates mechanically by malgnetostriction when stimulated magnetica y by the said field, and means in the circuit for utilizing the Eower when the vibrator, vfreely vibrating mec anically, responds magnetestrietively, renderin the power in certain parts of the circuit critical. as to frequency or frequencies near the free frequency of the vibrator.

- $9 In testimony whereof, I have hereunto subscribed my ne. 

